In a vehicle with trailer, excessive speed may cause fishtailing of the trailer about the vertical axis. Such fishtailing generally occurs only above a so-called critical speed, which is a function of the constructive properties and the loading of the trailer, in particular. The combination is instable above the critical speed.
From German Published Patent Application No. 100 31 266, it is known to detect fishtailing of the trailer by analyzing sensor data and to activate the vehicle or trailer brakes automatically, i.e., without involvement of the driver, in case of critical fishtailing of the trailer. The wheels of the vehicle or trailer may be braked both symmetrically (with equal force on the right and left) and also individually. Furthermore, it is known to dampen trailer fishtailing with the aid of automatic steering interventions in an active front or rear axle steering system. To detect the situation, a plurality of driving state variables such as the transverse acceleration or the yaw rate of the vehicle are normally analyzed in the process. In the mentioned methods a braking intervention is basically implemented whenever when a critical driving situation has been detected and a trailer is hooked up.
A particular problem in this context is the trailer detection. It is known, for instance, to detect a trailer by analyzing the electrical trailer connection. However, not all trailer types have an electrical connection and can be detected in this manner. Moreover, an electrical defect in the electrical system of the trailer could lead to a faulty detection. In this case the automatic stabilizing function would implement a braking operation even without a trailer being present, or it would not implement a braking operation although a trailer is hooked up.